Third of EU referendum voters won’t make up their minds until week before poll

Up to 30% of people will change the way they vote or make up their minds in the week before the 23 June Brexit referendum, with half of these only deciding finally on polling day, according to research by academics at the London School of Economics.

The findings, in a report sponsored by Opinium and Lansons strategic consultancy, suggest that the result could swing either way – depending on whether it is the Remain or Leave camp that convinces the most undecided voters in the final 12 days of the campaign.

The research, headed by Michael Bruter, professor of political science at the LSE, comes as the latest Opinium/Observer poll shows the outcome remains on a knife-edge. The poll puts Remain on 44%, Leave on 42% and those who say they don’t know how they will vote on 13%.

The LSE work is based on studies of voter behaviour in recent elections and referendums in 25 countries including the UK. Academics used panel studies and other interview and investigative methods to probe the psychological processes driving voters’ decisions.

The report, The Impact of Brexit on Consumer Behaviour, states that many voters are “very worried” about making the wrong decision and are therefore prone to changing their minds or leaving their choice until close to the actual moment they cast their vote. “We consistently find that 20-30% of voters either change their mind within a week of casting their ballot, about half of them on election day itself,” the report says.

Bruter said that experience showed that the proportions of late deciders and switches tended to be higher in referendums than in general elections. The way people vote is also more difficult to predict than in general elections because decisions are less tied to traditional party loyalties.

Explaining why people decide late or switch their vote close to or on polling day, he said: “This is the period when the campaign reaches its climax and most people not really interested in politics but still voting will only pay close attention to the vote at this very late time.

“In that last week, emotions run at their highest and when the vote starts feeling concrete and voters sense the atmosphere of the election. Before that, people offer more ‘selfish’ or unreflected opinions on what outcome they think is best, but it is only in the final week that the vote feels less abstract and more ‘real’ to them.

“It is the period when people suddenly declare being aware of a sense of responsibility on their shoulders as the solemnity of the vote makes them inhabit their ‘role’ as citizens. As a result, they become significantly more sociotropic – interested in what is best for the country, and not just for them – and feel that they have a collective responsibility to use their vote for the greater good.” He added: “For many people those factors are specifically heightened on the day of the vote when they physically enter the space of a polling station. Many voters are highly sensitive to the special atmosphere of the vote (especially, depending on context, when queues or the behaviour of other fellow citizens around them makes them feel that they are part of an important democratic moment), which is why so many change or make up their minds only on election day itself.”

The report says that arguments put forward by the Leave camp are met by voters with more scepticism than those advanced by those in Remain, even among those who say they back Brexit.

The Opinium/Observer poll was conducted according to the company’s new methodology, using a system that corrects what the pollsters say is a bias towards “socially conservative” voters in online polls. It shows 46% of Tory voters backing staying in the EU against 43% who want to leave and 63% of Labour voters staying in against 28% who want to leave. The figures for Ukip are 93% and 5%. When undecided voters were “nudged” to say which side they were leaning towards 38% said they were leaning to Remain and 26% to Leave.

Opinium Research carried out an online survey of 2,009 UK adults aged 18 and over from 7 to 10 June 2016. Results have been weighted to nationally representative criteria.